Problems may arise due to errors with:

  • Electrode function
  • Standards
  • Samples
  • Technique

Follow the steps below to isolate the source of the problem.

Electrode Function:

For pH, there should be a difference of 150 to 210 mV between pH 4 and 7, as well as between pH 7 and 10. Observing the mV values provides the best means for checking electrode performance. mV values are recorded during the calibration procedure. Check calibration values in the .glp file, or follow the procedure in Calibrating WQ-PH Smart USB Sensor.

If the mV difference is not within the normal range, follow the procedures described in WQ-PH Smart USB Sensor Maintenance.

If the electrode slope is still outside the normal range after this procedure, contact NexSens Customer Support for assessment.


The quality of results depends greatly upon the quality of the standards used. Use fresh standards when problems arise; it could save hours of troubleshooting. Errors may result from contamination of prepared standards.

Keep all standards tightly covered when not in use.


If the electrodes work properly in standards, but not in samples, there may be interfering ions, complexing agents, or substances which could affect responses. If possible, determine the composition of the samples and use the appropriate complexing agents for interfering ions.

Check that the value of the solution is within the operating range of the probe.

Be sure that the expected concentration of the sample is within the measurement range of the probe.


Closely follow the methods described in WQ-PH Smart USB Sensor Measurement Techniques.


REV: 13H31

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